Conventionally, continuous filaments of glass are manufactured by fiberizing streams of molten glass emanating and drawn from outlet orifices or tips located at the bottom or tip plate of a bushing. The bushing is usually made of a heat resistant material and may be fed with glass either intermittently or continuously in an amount which is dependent upon the quantity of glass being fiberized by the bushing. Under rare circumstances the bushing may be fed by melting a plurality of parallel glass rods whose ends are continuously shifted towards a heating device. However, the foregoing description presupposes that the fiberizing bushing is continuously fed with glass. Molten glass flowing from the orificees or tips form a spinning cone or filament generating cone on the outside of each of the tips. The molten glass is thus divided into individual streams and forms glass filaments that are continuously drawn out by a suitable device such as a drawing drum or winder. Subsequently, the glass filaments may be further processed in order to obtain a desired final product.
It is also well known, as illustrated by German Patent Specification (DOS) No. 2,460,170 and U.S. Pat. No. 3,248,192, to conduct a gas or gas mixture, such as steam, promoting the treatment and/or drawing of filaments, to area adjoining the tips, i.e., the fiberization zone. The fiberization zone, of course, is located downstream of the tips in the direction that the filaments are being drawn and is exposed to the radiant heat of the bushing.
In order to prevent a wetting of the outside surface of the tips by the glass, DOS No. 2,211,150 discloses a method and apparatus which conducts a material containing carbon or a substance having similar characteristics to the fiberization zone. A gas or gas mixture comprising an inert gas and a comparatively small quantity of an organic gas or hydrocarbon gas aids in conducting the carbon-containing material to the tips where it may be deposited on surfaces which are not to be wetted by glass. When the two gases are decomposed by heat radiating from the busing, a hydrogen component is also released in the region of the glass streams emanating from the bushing. The generation and feed of the gas or gas mixture is effected by means of flat tubes which run longitudinally along the bushing. The flat tubes may be disposed oblique to the plane of the filaments and have upper bends which are contiguous to the tips. The upper bends have outlet slits which are closest to the tips and hence the hottest region in the fiberization zone.
The gas flow generating flat tubes are shaped like a flattened radiator-like distributor tube and unfortunately the hottest constituents of the gases tend to rise towards the slits while the colder constituents of the gases tend to sink in the tubes. Thus, the gases are distributed in the tubes such that the coldest parts of the gases tend to collect away from the distributor slits and only the substantially decomposed hot constituents of the gases flow out of the distributor slits. This is a considerable disadvantage because the colder, non-vaporizing gases may collect in the lower part of the tubes and may not be consumed continuously. Furthermore, the areas of the tubes which are closest to the hottest region of the fiberization zone carry the hottest constituents of the gases and are thus exposed to premature thermal degradation or destruction. Disassociation of the gases is also promoted by this type of arrangement.
In addition, gas distribution problems occur with such a method. The closer the gas emanating from the slits is to the tips and hence to filaments which may not have hardened, the less space and time are available for the gas to diffuse in all directions. This is caused by the fact that a column of glass filaments continuously being taken off the bushing at a high velocity creates a continuous air stream moving in a direction which is parallel to the direction in which the filaments are being drawn. This continuous air stream picks up the gas as soon as the gas comes into the area of the air stream. Thus, an even distribution of the generated gas across the entire area of the bushing cannot be ensured.